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// Copyright 2009 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package xml

import (
        "bytes"
        "errors"
        "reflect"
        "strconv"
        "strings"
)

// BUG(rsc): Mapping between XML elements and data structures is inherently flawed:
// an XML element is an order-dependent collection of anonymous
// values, while a data structure is an order-independent collection
// of named values.
// See package json for a textual representation more suitable
// to data structures.

// Unmarshal parses the XML-encoded data and stores the result in
// the value pointed to by v, which must be an arbitrary struct,
// slice, or string. Well-formed data that does not fit into v is
// discarded.
//
// For example, given these definitions:
//
//      type Email struct {
//              Where string `xml:",attr"`
//              Addr  string
//      }
//
//      type Result struct {
//              XMLName xml.Name `xml:"result"`
//              Name    string
//              Phone   string
//              Email   []Email
//              Groups  []string `xml:"group>value"`
//      }
//
//      result := Result{Name: "name", Phone: "phone", Email: nil}
//
// unmarshalling the XML input
//
//      <result>
//              <email where="home">
//                      <addr>gre@example.com</addr>
//              </email>
//              <email where='work'>
//                      <addr>gre@work.com</addr>
//              </email>
//              <name>Grace R. Emlin</name>
//              <group>
//                      <value>Friends</value>
//                      <value>Squash</value>
//              </group>
//              <address>123 Main Street</address>
//      </result>
//
// via Unmarshal(data, &result) is equivalent to assigning
//
//      r = Result{
//              xml.Name{Local: "result"},
//              "Grace R. Emlin", // name
//              "phone",          // no phone given
//              []Email{
//                      Email{"home", "gre@example.com"},
//                      Email{"work", "gre@work.com"},
//              },
//              []string{"Friends", "Squash"},
//      }
//
// Note that the field r.Phone has not been modified and
// that the XML <address> element was discarded. Also, the field
// Groups was assigned considering the element path provided in the
// field tag.
//
// Because Unmarshal uses the reflect package, it can only assign
// to exported (upper case) fields.  Unmarshal uses a case-sensitive
// comparison to match XML element names to tag values and struct
// field names.
//
// Unmarshal maps an XML element to a struct using the following rules.
// In the rules, the tag of a field refers to the value associated with the
// key 'xml' in the struct field's tag (see the example above).
//
//   * If the struct has a field of type []byte or string with tag
//      ",innerxml", Unmarshal accumulates the raw XML nested inside the
//      element in that field.  The rest of the rules still apply.
//
//   * If the struct has a field named XMLName of type xml.Name,
//      Unmarshal records the element name in that field.
//
//   * If the XMLName field has an associated tag of the form
//      "name" or "namespace-URL name", the XML element must have
//      the given name (and, optionally, name space) or else Unmarshal
//      returns an error.
//
//   * If the XML element has an attribute whose name matches a
//      struct field name with an associated tag containing ",attr" or
//      the explicit name in a struct field tag of the form "name,attr",
//      Unmarshal records the attribute value in that field.
//
//   * If the XML element contains character data, that data is
//      accumulated in the first struct field that has tag "chardata".
//      The struct field may have type []byte or string.
//      If there is no such field, the character data is discarded.
//
//   * If the XML element contains comments, they are accumulated in
//      the first struct field that has tag ",comments".  The struct
//      field may have type []byte or string.  If there is no such
//      field, the comments are discarded.
//
//   * If the XML element contains a sub-element whose name matches
//      the prefix of a tag formatted as "a" or "a>b>c", unmarshal
//      will descend into the XML structure looking for elements with the
//      given names, and will map the innermost elements to that struct
//      field. A tag starting with ">" is equivalent to one starting
//      with the field name followed by ">".
//
//   * If the XML element contains a sub-element whose name matches
//      a struct field's XMLName tag and the struct field has no
//      explicit name tag as per the previous rule, unmarshal maps
//      the sub-element to that struct field.
//
//   * If the XML element contains a sub-element whose name matches a
//      field without any mode flags (",attr", ",chardata", etc), Unmarshal
//      maps the sub-element to that struct field.
//
//   * If the XML element contains a sub-element that hasn't matched any
//      of the above rules and the struct has a field with tag ",any",
//      unmarshal maps the sub-element to that struct field.
//
//   * A struct field with tag "-" is never unmarshalled into.
//
// Unmarshal maps an XML element to a string or []byte by saving the
// concatenation of that element's character data in the string or
// []byte. The saved []byte is never nil.
//
// Unmarshal maps an attribute value to a string or []byte by saving
// the value in the string or slice.
//
// Unmarshal maps an XML element to a slice by extending the length of
// the slice and mapping the element to the newly created value.
//
// Unmarshal maps an XML element or attribute value to a bool by
// setting it to the boolean value represented by the string.
//
// Unmarshal maps an XML element or attribute value to an integer or
// floating-point field by setting the field to the result of
// interpreting the string value in decimal.  There is no check for
// overflow.
//
// Unmarshal maps an XML element to an xml.Name by recording the
// element name.
//
// Unmarshal maps an XML element to a pointer by setting the pointer
// to a freshly allocated value and then mapping the element to that value.
//
func Unmarshal(data []byte, v interface{}) error {
        return NewDecoder(bytes.NewBuffer(data)).Decode(v)
}

// Decode works like xml.Unmarshal, except it reads the decoder
// stream to find the start element.
func (d *Decoder) Decode(v interface{}) error {
        return d.DecodeElement(v, nil)
}

// DecodeElement works like xml.Unmarshal except that it takes
// a pointer to the start XML element to decode into v.
// It is useful when a client reads some raw XML tokens itself
// but also wants to defer to Unmarshal for some elements.
func (d *Decoder) DecodeElement(v interface{}, start *StartElement) error {
        val := reflect.ValueOf(v)
        if val.Kind() != reflect.Ptr {
                return errors.New("non-pointer passed to Unmarshal")
        }
        return d.unmarshal(val.Elem(), start)
}

// An UnmarshalError represents an error in the unmarshalling process.
type UnmarshalError string

func (e UnmarshalError) Error() string { return string(e) }

// Unmarshal a single XML element into val.
func (p *Decoder) unmarshal(val reflect.Value, start *StartElement) error {
        // Find start element if we need it.
        if start == nil {
                for {
                        tok, err := p.Token()
                        if err != nil {
                                return err
                        }
                        if t, ok := tok.(StartElement); ok {
                                start = &t
                                break
                        }
                }
        }

        if pv := val; pv.Kind() == reflect.Ptr {
                if pv.IsNil() {
                        pv.Set(reflect.New(pv.Type().Elem()))
                }
                val = pv.Elem()
        }

        var (
                data         []byte
                saveData     reflect.Value
                comment      []byte
                saveComment  reflect.Value
                saveXML      reflect.Value
                saveXMLIndex int
                saveXMLData  []byte
                saveAny      reflect.Value
                sv           reflect.Value
                tinfo        *typeInfo
                err          error
        )

        switch v := val; v.Kind() {
        default:
                return errors.New("unknown type " + v.Type().String())

        case reflect.Interface:
                // TODO: For now, simply ignore the field. In the near
                //       future we may choose to unmarshal the start
                //       element on it, if not nil.
                return p.Skip()

        case reflect.Slice:
                typ := v.Type()
                if typ.Elem().Kind() == reflect.Uint8 {
                        // []byte
                        saveData = v
                        break
                }

                // Slice of element values.
                // Grow slice.
                n := v.Len()
                if n >= v.Cap() {
                        ncap := 2 * n
                        if ncap < 4 {
                                ncap = 4
                        }
                        new := reflect.MakeSlice(typ, n, ncap)
                        reflect.Copy(new, v)
                        v.Set(new)
                }
                v.SetLen(n + 1)

                // Recur to read element into slice.
                if err := p.unmarshal(v.Index(n), start); err != nil {
                        v.SetLen(n)
                        return err
                }
                return nil

        case reflect.Bool, reflect.Float32, reflect.Float64, reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr, reflect.String:
                saveData = v

        case reflect.Struct:
                typ := v.Type()
                if typ == nameType {
                        v.Set(reflect.ValueOf(start.Name))
                        break
                }

                sv = v
                tinfo, err = getTypeInfo(typ)
                if err != nil {
                        return err
                }

                // Validate and assign element name.
                if tinfo.xmlname != nil {
                        finfo := tinfo.xmlname
                        if finfo.name != "" && finfo.name != start.Name.Local {
                                return UnmarshalError("expected element type <" + finfo.name + "> but have <" + start.Name.Local + ">")
                        }
                        if finfo.xmlns != "" && finfo.xmlns != start.Name.Space {
                                e := "expected element <" + finfo.name + "> in name space " + finfo.xmlns + " but have "
                                if start.Name.Space == "" {
                                        e += "no name space"
                                } else {
                                        e += start.Name.Space
                                }
                                return UnmarshalError(e)
                        }
                        fv := sv.FieldByIndex(finfo.idx)
                        if _, ok := fv.Interface().(Name); ok {
                                fv.Set(reflect.ValueOf(start.Name))
                        }
                }

                // Assign attributes.
                // Also, determine whether we need to save character data or comments.
                for i := range tinfo.fields {
                        finfo := &tinfo.fields[i]
                        switch finfo.flags & fMode {
                        case fAttr:
                                strv := sv.FieldByIndex(finfo.idx)
                                // Look for attribute.
                                for _, a := range start.Attr {
                                        if a.Name.Local == finfo.name {
                                                copyValue(strv, []byte(a.Value))
                                                break
                                        }
                                }

                        case fCharData:
                                if !saveData.IsValid() {
                                        saveData = sv.FieldByIndex(finfo.idx)
                                }

                        case fComment:
                                if !saveComment.IsValid() {
                                        saveComment = sv.FieldByIndex(finfo.idx)
                                }

                        case fAny:
                                if !saveAny.IsValid() {
                                        saveAny = sv.FieldByIndex(finfo.idx)
                                }

                        case fInnerXml:
                                if !saveXML.IsValid() {
                                        saveXML = sv.FieldByIndex(finfo.idx)
                                        if p.saved == nil {
                                                saveXMLIndex = 0
                                                p.saved = new(bytes.Buffer)
                                        } else {
                                                saveXMLIndex = p.savedOffset()
                                        }
                                }
                        }
                }
        }

        // Find end element.
        // Process sub-elements along the way.
Loop:
        for {
                var savedOffset int
                if saveXML.IsValid() {
                        savedOffset = p.savedOffset()
                }
                tok, err := p.Token()
                if err != nil {
                        return err
                }
                switch t := tok.(type) {
                case StartElement:
                        consumed := false
                        if sv.IsValid() {
                                consumed, err = p.unmarshalPath(tinfo, sv, nil, &t)
                                if err != nil {
                                        return err
                                }
                                if !consumed && saveAny.IsValid() {
                                        consumed = true
                                        if err := p.unmarshal(saveAny, &t); err != nil {
                                                return err
                                        }
                                }
                        }
                        if !consumed {
                                if err := p.Skip(); err != nil {
                                        return err
                                }
                        }

                case EndElement:
                        if saveXML.IsValid() {
                                saveXMLData = p.saved.Bytes()[saveXMLIndex:savedOffset]
                                if saveXMLIndex == 0 {
                                        p.saved = nil
                                }
                        }
                        break Loop

                case CharData:
                        if saveData.IsValid() {
                                data = append(data, t...)
                        }

                case Comment:
                        if saveComment.IsValid() {
                                comment = append(comment, t...)
                        }
                }
        }

        if err := copyValue(saveData, data); err != nil {
                return err
        }

        switch t := saveComment; t.Kind() {
        case reflect.String:
                t.SetString(string(comment))
        case reflect.Slice:
                t.Set(reflect.ValueOf(comment))
        }

        switch t := saveXML; t.Kind() {
        case reflect.String:
                t.SetString(string(saveXMLData))
        case reflect.Slice:
                t.Set(reflect.ValueOf(saveXMLData))
        }

        return nil
}

func copyValue(dst reflect.Value, src []byte) (err error) {
        // Helper functions for integer and unsigned integer conversions
        var itmp int64
        getInt64 := func() bool {
                itmp, err = strconv.ParseInt(string(src), 10, 64)
                // TODO: should check sizes
                return err == nil
        }
        var utmp uint64
        getUint64 := func() bool {
                utmp, err = strconv.ParseUint(string(src), 10, 64)
                // TODO: check for overflow?
                return err == nil
        }
        var ftmp float64
        getFloat64 := func() bool {
                ftmp, err = strconv.ParseFloat(string(src), 64)
                // TODO: check for overflow?
                return err == nil
        }

        // Save accumulated data.
        switch t := dst; t.Kind() {
        case reflect.Invalid:
                // Probably a comment.
        default:
                return errors.New("cannot happen: unknown type " + t.Type().String())
        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                if !getInt64() {
                        return err
                }
                t.SetInt(itmp)
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                if !getUint64() {
                        return err
                }
                t.SetUint(utmp)
        case reflect.Float32, reflect.Float64:
                if !getFloat64() {
                        return err
                }
                t.SetFloat(ftmp)
        case reflect.Bool:
                value, err := strconv.ParseBool(strings.TrimSpace(string(src)))
                if err != nil {
                        return err
                }
                t.SetBool(value)
        case reflect.String:
                t.SetString(string(src))
        case reflect.Slice:
                if len(src) == 0 {
                        // non-nil to flag presence
                        src = []byte{}
                }
                t.SetBytes(src)
        }
        return nil
}

// unmarshalPath walks down an XML structure looking for wanted
// paths, and calls unmarshal on them.
// The consumed result tells whether XML elements have been consumed
// from the Decoder until start's matching end element, or if it's
// still untouched because start is uninteresting for sv's fields.
func (p *Decoder) unmarshalPath(tinfo *typeInfo, sv reflect.Value, parents []string, start *StartElement) (consumed bool, err error) {
        recurse := false
Loop:
        for i := range tinfo.fields {
                finfo := &tinfo.fields[i]
                if finfo.flags&fElement == 0 || len(finfo.parents) < len(parents) {
                        continue
                }
                for j := range parents {
                        if parents[j] != finfo.parents[j] {
                                continue Loop
                        }
                }
                if len(finfo.parents) == len(parents) && finfo.name == start.Name.Local {
                        // It's a perfect match, unmarshal the field.
                        return true, p.unmarshal(sv.FieldByIndex(finfo.idx), start)
                }
                if len(finfo.parents) > len(parents) && finfo.parents[len(parents)] == start.Name.Local {
                        // It's a prefix for the field. Break and recurse
                        // since it's not ok for one field path to be itself
                        // the prefix for another field path.
                        recurse = true

                        // We can reuse the same slice as long as we
                        // don't try to append to it.
                        parents = finfo.parents[:len(parents)+1]
                        break
                }
        }
        if !recurse {
                // We have no business with this element.
                return false, nil
        }
        // The element is not a perfect match for any field, but one
        // or more fields have the path to this element as a parent
        // prefix. Recurse and attempt to match these.
        for {
                var tok Token
                tok, err = p.Token()
                if err != nil {
                        return true, err
                }
                switch t := tok.(type) {
                case StartElement:
                        consumed2, err := p.unmarshalPath(tinfo, sv, parents, &t)
                        if err != nil {
                                return true, err
                        }
                        if !consumed2 {
                                if err := p.Skip(); err != nil {
                                        return true, err
                                }
                        }
                case EndElement:
                        return true, nil
                }
        }
        panic("unreachable")
}

// Skip reads tokens until it has consumed the end element
// matching the most recent start element already consumed.
// It recurs if it encounters a start element, so it can be used to
// skip nested structures.
// It returns nil if it finds an end element matching the start
// element; otherwise it returns an error describing the problem.
func (d *Decoder) Skip() error {
        for {
                tok, err := d.Token()
                if err != nil {
                        return err
                }
                switch tok.(type) {
                case StartElement:
                        if err := d.Skip(); err != nil {
                                return err
                        }
                case EndElement:
                        return nil
                }
        }
        panic("unreachable")
}